From: pcw@access.digex.net (Peter Wayner)
Date: Fri, 15 Dec 1995 03:21:17 +0800
To: hallam@w3.org
Subject: EMF loopholes and [Re: Kocher's RSA attack]
Message-ID: <v02130507acf621e14fbc@[199.125.128.5]>
MIME-Version: 1.0
Content-Type: text/plain



>
>A conclusion which might be reached is that smartcards should
>in future contain
>contain a timer which is started at the beginnin of every cryptographic
>operation and a delay loop introduced to ensure that the time taken is always
>the same. The alternative of attempting to ensure that equal processing is
>spent on each cycle threatens an infinite regress into second and third order
>effects, eg frequency of page faults. Covert channel analysis is bad enough
>as it is.
>

I remember the first computer I built had a neat wireless "sound
card" built in. The radio waves generated by the processor could
be modified by choosing the instructions executed. So you could
get sound for your computer games by putting a radion next to
the machine! The delay loops for the games contained multiple
paths for different sounds. It was actually pretty good for the
time.

This leads me to believe that a delay loop might not be good
enough. The leakage from the smart card could be enough to
identify when the card entered the delay loop. The difference
between the signal could be significant.

Just a thought.

-Peter